Field of the Invention
The present invention relates to a holding sealing material, a method for manufacturing a holding sealing material, an exhausted gas purifying apparatus, and a method for manufacturing an exhaust gas purifying apparatus.
Discussion of the Background
Exhaust gases that are emitted from internal combustion engines such as diesel engines contain particulate matters (hereinafter, also referred to as PMs). PMs that are harmful to the environment and human body have been recently recognized as problems. Exhaust gases also contain harmful gases such as CO, HC, and NOx. Thus, adverse effects on the environment and human body by these harmful gases are also being worried.
For collecting PMs and purifying those harmful gases in exhaust gases, various exhaust gas purifying apparatuses are proposed. Such an exhaust gas purifying apparatus includes an exhaust gas treating body formed of porous ceramic such as silicon carbide or cordierite, a casing accommodating the exhaust gas treating body, and a holding sealing material placed between the exhaust gas treating body and the casing. The holding sealing material is mainly used for preventing the exhaust gas treating body from breaking by a collision, due to vibration or impacts during driving a car or the like, with the casing that covers the outer periphery of the exhaust gas treating body; and for preventing exhaust gases from leaking from a gap between the exhaust gas treating body and the casing.
An internal combustion engine is typically driven at a ratio close to the theoretical air fuel ratio for improving fuel economy, and thus tends to increase the temperature and the pressure of exhaust gases. When exhaust gases with a high temperature and a high pressure are carried into an exhaust gas purifying apparatus, due to the difference between the coefficient of thermal expansion of an exhaust gas treating body and that of a casing, the size of a gap between the exhaust gas treating body and the casing is changed. Thus, holding sealing materials are required to have a stable holding ability that is not affected by changes of the size of the gap. In addition, holding sealing materials are being more and more required to have thermal insulation performance for thermally insulating an exhaust gas treating body so that the exhaust gas treating body can efficiently exhibit the exhaust gas purifying performance.
Recently, a new configuration of a holding sealing material is adopted in which a holding sealing material with a larger thickness is used to enhance the thermal insulation performance. In such a holding sealing material, the repulsive force of inorganic fibers, which imparts holding ability to the holding sealing material, needs to be ensured by increasing the weight per unit area of the holding sealing material.
However, the larger the thickness of the holding sealing material is, the less the holding sealing material tends to achieve a sufficient peeling strength in needling carried out in a manufacturing process for increasing the peeling strength in the thickness direction. Such an insufficient peeling strength may cause the holding sealing material to have a significant shear deformation when an exhaust gas treating body wound with the holding sealing material is stuffed into a casing.
Another configuration of a holding sealing material is that plural mats each having the same weight as a conventional holding sealing material are used to increase the total weight, instead of changing the thickness of the holding sealing material. As such an example, a holding sealing material (JP-A 2007-218221) having the following configuration is disclosed. In the holding sealing material, plural mats that each have a pair of fitting portions and thermal insulation performance are layered. The plural mats each have a proper length for being wound without gaps, and the pair of fitting portions of the mats is configured to fit to each other when the mats are layered and wound around a monolith.
In addition, holding sealing materials having plural mats layered and sewn by a sewing machine to be fixed are disclosed (JP-A 2009-264186 and JP-A 2009-264187).